The present invention concerns chairs having a reclineable back, and more particularly concerns chairs having a reclineable back and a forwardly movable/tiltable seat that moves with a synchronous movement as the back is reclined.
Modern customers and chair purchasers demand a wide variety of chair options and features, and a number of options and features are often designed into chair seats. However, improvement in seats is desired so that a seated user's weight is adequately supported on the chair seat, but simultaneously so that the thigh area of a seated user is comfortably, adjustably supported in a manner that adequately allows for major differences in the shape and size of a seated user's buttocks and thighs. Additionally, it is important that such options and features be incorporated into the chair construction in a way that minimizes the number of parts and maximizes the use of common parts among different options, maximizes efficiencies of manufacturing and assembling, maximizes ease of adjustment and the logicalness of adjustment control positioning, and yet that results in a visually pleasing design.
More specifically, in regard to synchrotilt chairs where the seat and the back pivot with synchronized angular movements, many synchrotilt chairs have been designed to pivot seats rearwardly as a user reclines. However, often these known seat constructions pivot about a seat pivot axis located rearward of a front edge of the seat. The result is that the knees of a seated user are lifted, resulting in undesired pressure on the seated user's thighs upon recline. Designing a flexible front lip into the seat does not fully resolve the undesired thigh pressure since the thighs are not supported only at a front lip of the seat, but instead are supported along at least about half of the seat. Locating a flexible zone substantially rearwardly in a seat, such as rearward of the hip joint of a seated user, also does not resolve the situation since the weight of a seated user's upper torso tends to cause a seated user to slip/slide downwardly and forwardly off of a chair back when the chair back is reclined. This in turn causes the seated user to slide forward and off of the seat unless the seat includes a rear zone shaped and oriented to support the seated user against such forward slip/slide movement. The problem is compounded by the fact that the hip joint of different seated user's are not always located in the same relative location on the chair seat, such that one seat design may work well for one seated user, but not for another seated user.
Even if the thigh support problems of a seat construction are solved, it is desired to improve the location of the seat construction relative to its surroundings. For example, a synchrotilt chair is described in U.S. Pat. Nos. 5,050,931; 4,744,603; 4,776,633; and 5,567,012 (to Knoblock et al.) having a base assembly with a control, a reclineable back pivoted to the control, and a seat operably mounted to the back and control for synchronous motion as the back is reclined. This prior art chair incorporates a semi-rigid flexible shell that, in combination with the chair support structure, provides a highly-controlled postural support during the body movements associated with tasks/work (e.g., when the back is in an upright position) and during the body movements associated with recline/relaxation (e.g., when the chair is in a reclined position). This prior art chair moves a seated user's upper body away from the user's work surface as the user reclines, thus providing the user with more area to stretch. However, we have discovered that often users want to remain close to their work surface and want to continue to work at the work surface, even while reclining and relaxing their body and while having continued postural support. In order to do this in the synchrotilt chair of U.S. Pat. No. 5,050,931, users must scoot their chair forwardly after they recline so that they can still easily reach their work surface. They must also push away when they move back to an upright position to avoid being pushed against their work surface. "Scooting" back and forth once or twice is perhaps not a serious problem, but often users, such as office workers using computers, are constantly moving between upright and reclined positions, such that the process of repeatedly scooting back and forth becomes annoying and disconcerting. In fact, moving around and not staying in a single static position is important to good back health in workers whose jobs require a lot of sitting.
Another disadvantage of moving a seated user's upper body significantly rearwardly upon recline is that the user's overall center of gravity moves rearward. By providing a more constant center of gravity, it is possible to design a reclineable chair having greater recline or height adjustment without sacrificing the overall stability of the chair. Also, reclineable chairs that move a seated user's upper body significantly rearwardly have a relatively large footprint, such that these chairs may bump into furniture or a wall when used in small offices or in a compact work area. Still another disadvantage is that large springs are required in these existing reclineable chairs for back support, which springs are difficult to adjust due to the forces generated by the springs. However, the tension of these springs preferably should be adjustable so that heavier and lighter weight users can adjust the chair to provide a proper amount of support.
Concurrently, seated users want to be able to easily adjust the spring tension for providing support to the back during recline. Not only do heavier/larger people need greater/firmer back support than lighter/smaller people, but the amount of support required changes at a greater rate during recline. Specifically, lighter/smaller people need a lesser initial level of support as they begin to recline and need a moderately increased level of support as they continue to recline; while heavier/larger people need a significantly higher minimum initial level of support as they begin to recline and need a significantly increased level of support as they continue to recline. Restated, it is desirable to provide a chair that is easily adjustable in its initial level of support to the back during initial recline and that automatically also adjusts the rate of increase in support during recline. Further, it is desirable to provide a mechanism to allow such an easy adjustment (1) while seated; (2) by a relatively weaker person; (3) using easily manipulatable adjustment controls; and (4) while doing so with a control that is not easily damaged by a relatively strong person who may "overtorque" the control. Further, a compact spring arrangement is desired to provide optimal appearance and to minimize material cost and part size.
Accordingly, a chair construction solving the aforementioned problems is desired.